The invention relates to a method of manufacturing sheet stacks for electromagnetic assemblies, consisting of ferromagnetic material, and for the manufacture of electromagnetic assemblies provided with such sheet stacks and one additional component. The invention also relates to sheet stacks and components manufactured according to these methods.
Electromagnetic assemblies which operate with alternating fields, frequently have iron cores of ferromagnetic material, which serve the purpose of guiding magnetic fields at every point where no air gaps are provided or desired. In order to avoid eddy current and eddy current losses, these iron cores are predominantly assembled from a plurality of sheet metal blanks, which are obtained by stamping from sheet metal panels or strips, which consist for example of steel or iron plates e.g. 0.35 to 1.00 mm thick, and which are insulated from one another by a lacquer coating, an oxide layer or other means. The insulation can be applied to the bands, strips or panels either already in the rolling mill to the sheet metal band or strip, or subsequently in a special coating plant, and nowadays usually consists of an extremely thin silica phosphate layer, which is applied as the sheets are rolled out.
In addition it is frequently desired to connect the individual stamped blanks together to form a solid sheet stack. This is achieved e.g. by the use of form-fitting or positive-locking mechanical means or simply by surrounding the finished sheet stacks or cores by a winding, in which case it is however also necessary electrically to insulate the windings from the core.
In order to avoid such connection methods, which are in fact comparatively cost-effective, but cannot always be used, it is already known (DE 31 10 339 C2) firstly to provide strips manufactured from silicated magnetic steel sheet preferably on both sides with additional adhesive layers, which consist for example of a pre-hardened duroplastic adhesive, and if necessary are applied in the rolling mill in a complex, expensive working step. The sheet stacks are then produced by stamping out sheet metal blanks or lamellae from such sheet metal strips drawn off from coils (drums), and these are then combined into stacks and thereafter securely fastened together by heating with simultaneous pressure, in order to form a mechanically secure sheet stack. Then the finished sheet stacks are additionally provided with a coating of an epoxy resin or the like, in order to provide the cut edges of the sheets revealed during cutting subsequently with an anti-corrosion layer. This method is therefore in fact suitable for manufacturing compact, high-quality sheet stacks, but due to the high technical outlay and the necessarily high manufacturing costs for coating the sheets with adhesive, is only infrequently used. A further disadvantage is that the off-cuts occurring during stamping of the sheet metal blanks are provided with an adhesive layer, which prevents properly categorized recycling of the sheet metal off-cuts, and therefore should be avoided for reasons of environmental protection.
Sheet stacks of the type described are in addition frequently connected together with other components in order to form finished assemblies. In this respect it is for example known (DE 40 21 591 C2) to surround the individual parts of the stator of an electric motor, particularly a sheet stack and the associated windings, with a casting resin in a shaping tool, so that on the one hand the windings are electrically insulated and on the other hand a cohesive composite member is obtained. Correspondingly, it is known in manufacturing the rotors of electric motors (DE 43 38 913 A1) firstly to assemble the associated shafts, sheet stacks, windings and commutators loosely together, and then to provide them with a plastic covering in a shaping tool by injection molding, injection pressure or the like. This does in fact give rise to the advantage that the sheet stack is subsequently provided with an insulation or an anti-corrosion layer on the cut edges revealed during stamping of the plates. In all these methods however a condition is the presence of finished sheet stacks produced in the way explained above.
It is an object of the present invention to provide a method for manufacturing sheet stacks and electromagnetic assemblies provided with sheet stacks, which enables the use of simple, cost-effective plates, whose off-cuts can be disposed of in an environmentally acceptable manner, and which further requires fewer individual steps than previously and therefore in particular leads to simplifications in manufacture of the assemblies. Moreover, a high degree of mechanical strength and a high degree of resistance to external or internal weathering influences is to be achieved.
According to the invention the method of manufacturing a sheet stack for electromagnetic assemblies, consisting of ferromagnetic material, comprises forming the sheet stack from raw magnetic steel sheets in a shaping tool without the use of spacers, if necessary with the help of positioning aids, and simultaneously introducing a hardenable mixture into the shaping tool in order to totally surround the sheet stack and to form an anti-corrosion layer and hardening or hardening out this casting compound according to the pressure-gelating method to connect the sheets together and to form the finished sheet stack in one single wording step.
According to the invention the method of manufacturing the electromagnetic assembly including at least one sheet stack and one additional component comprises making the finished sheet stack in accordance with the foregoing pressure-gelating method, connecting the finished sheet stack to the additional component to form the assembly and surrounding the assembly with the mixture in order to form the anti-corrosion layer.
Further advantageous features of the invention will become apparent from the sub-claims.
In a preferred embodiment of both methods according to the invention a pressure of from 2 to 10 mbar is maintained in the shaping tool. The assembly as a whole is preferably only provided with its final electrical, mechanical and/or geometric properties by means of the hardenable mixture and the hardenable mixture is advantageously a thermally hardenable mixture.
The invention may with advantage be used at every point where sheet stacks made of ferromagnetic material are required. The term xe2x80x9celectromagnetic assembliesxe2x80x9d therefore in particular comprises electrical motors on a basis of three-phase, synchronous and asynchronous current and parts thereof such for example as stators and runners as well as choke coils with iron cores, transformers and magnets, particularly load-raising or lifting magnets and parts thereof.